Lesson 104: Abacus flash sums practice past ten
Level 9, Mind Castle. Flash sums that go past ten. Can you get five in a row?
What your child does, card by card
Flash practice: past ten. Practice day! PlayBuddy opens the lesson: “Practice time. Let's get quicker and better.”
First a reminder (“8 + 7 + 5”): the beads build 8, 5, 15, 10 and 20, ring by ring, while your child watches. On the beads, one number at a time.
Try it: your child works out the columns 6 + 7 + 5 and 8 + 4 - 5 + 9, with a green ring on the next bead to move.
Flash sums in your head: the abacus is covered and the numbers appear one at a time, 1.1 seconds each (6 + 7 + 5, 9 + 8 + 3, 5 + 6 + 7 + 2, 8 + 4 - 5 + 9 and 7 + 7 + 7); your child adds them in the head and picks the total from 16, 18, 19, 20 and 21.
You're ready! Flash sums past ten.
What this lesson trains
10 answers in about five minutes. The tasks take 11 bead moves in all: 4 with a top bead and 7 with bottom beads. Numbers reach 18, so the tens rod and the ones rod work. Then 5 quick looks in your head. 4 of the 5 sums need a big friend (“+7 = +2 −5 +10”, “+4 = −6 +10”, “−5 = −10 +5” and “+9 = −1 +10”); the others use free beads.
It starts with doing: work out the columns 6 + 7 + 5 and 8 + 4 - 5 + 9.
The sum sheet
The lower window shows the column as a child would write it on paper: one number under another, the current line in yellow, ticks on the lines done. The abacus carries the running total from line to line.
What PlayBuddy and PlayType say
PlayBuddy: “One line at a time, top to bottom.”
Stars
10 answers: 1 slip still gives three stars; up to 2, two stars.